Composite structures made of fiber reinforced resin provide relatively strong structures that are light weight that have many applications such as but not limited to stiffeners for aircraft. One method of forming composite structures is with fibers that are pre-pregnanted (pre-preg) with resin. Once positioned in the desired shape, the fibers and resin are heated to cure the resin thereby bonding the fibers together to form the structure. In the aerospace industry it is common to make elongated stiffeners having various cross-sectional shapes that commonly define the stiffeners such as a hat, a C and a Z shaped stiffeners. One method of forming stiffeners is by laying up layers of fiber to form a flat preform. The preforms are then hot-drape formed or compression molded on a mandrel to create a desired cross-sectional shape. After hot-drape forming, the parts are either co-cured to a laminate or cured in an autoclave and secondary bonded/fastened to a structure. One limitation of the hot-drape method is that winkles commonly occur in corners when forming a desired cross-sectional shape (i.e. C shape, Z shape, hat shape, etc.) in a structure. The wrinkles can lead to an undesired weak point in the formed structure.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for methods of forming efficient and effective composite structures without wrinkles in the corners.